1. Field of the Invention
The present invention relates to a color processing apparatus for outputting a color chart, and to a color processing method.
2. Description of the Related Art
Along with the widespread use of devices for handling color images, applications such as outputting color images by using a plurality of printers at offices, and outputting created color images at transmitting and receiving destinations via a network are on the increase. In such a case, even if color image data is the same, reproduced colors can become different due to difference between characteristics of individual devices, eventually presenting a problem. This is because color representation method (e.g., Red-Green-Blue (RGB) or Cyan-Magenta-Yellow-blacK (CMYK)) and reproducible color range (hereinafter, the reproducible color range is referred to as “color gamut”) are varied from device to device.
Therefore, in order to match colors of devices with each other, it is necessary to perform color conversion processing to appropriately correct difference in color gamuts for each device in device-independent color space (Commission Internationale de l'Eclairage (CIE) L*a*b* Space (CIELAB) and CIE Color Appearance Model (CIECAM) 02). For instance, if a color image displayed on a monitor is output by a printer, a color gamut of a monitor is generally wider than a color gamut of a printer. In this case, color processing for converting colors which cannot be reproduced by the printer into colors which can be reproduced by the printer is needed
In recent years, as a color matching technique for matching the colors of devices with each other, a color management system (CMS) has been discussed. General CMS uses a profile (for instance, International Color Consortium (ICC) profile) which indicates device characteristics. For instance, a profile of a printer is created by printing a color chart including a predetermined color patch, measuring a print result with a dedicated measurement device, and then processing a measurement result in a computer where a dedicated program is executed. In the profile, a corresponding relationship between device-dependent color space and device-independent color space is described, and the color matching is realized by correcting colors of color images using the profile. Therefore, it is important to use an appropriate profile for realizing the color conversion processing with a high precision
On the other hand, device characteristics are different depending on viewing environments of an output product of color images. For instance, even if the same color images are output by the same device, colors perceived by humans are viewed differently between the cases where light sources in a room are a fluorescent light and an incandescent light. Thus, there is discussed a method for estimating a color appearance under a desired light source in order to correct color appearance variations resulting from such differences in viewing conditions of an image (e.g., Japanese Patent Application Laid-Open No. 2005-210646).
Conventionally, a profile was generated using a color chart of a particular color patch configuration which is not dependent on viewing conditions of an output product. However, if the viewing conditions of an image are changed, device characteristics, namely, a color gamut shape is also changed. As a result, there is a problem that a bias occurs in a distribution of the color patches of the color chart, and thus a color reproduction precision of the profile is lowered. Further, Japanese Patent Application Laid-Open No. 2005-210646 does not relate to a technique for suitably creating the color chart.